Electron beam wave signal frequency converter utilizing beam deflection and beam defocusing



R. ADLER Jan. 14, 1958 2,820,139 ELECTRON BEAM WAVE SIGNAL FREQUENCYCONVERTER UTILIZING BEAM DEFLECTION AND BEAM DEFOCUSING 3 Sheets-Sheet 1Filed NOV. 8, 1954 Ldud Circuit B5+ iii-Z 1 38 I" vil ROBERT ADLERINVENTOR.

HIS ATTORNEY.

Jan. 14, 1958 R. ADLER 2,820,139

ELECTRON BEAM WAVE SIGNAL FREQUENCY CONVERTER UTILIZING BEAM- DEFLECTIONAND BEAM DEFOCUSING FIGS HIS ATTORNEY.

R. ADLER Jan. 14, 1958 UTILIZING BEAM DEFLECTIONv AND BEAM DEFOCUSING 5Sheets-Sheet 3 Filed Nov. 8, 1954 6 6 e 4 B 326m m zoutom B M 7 a I mby! 4 6 w mow A e 7 0 330m 228.com mm Cu 9 E l.. 8 F O 9 3 B 5 3 i? A II, T F u W SIG E! E w n a w E m w mlfim n 8 G F ROBERT ADLER IN VEN TOR.

FIG. 9

HIS ATTORNEY.

United States atent ELECTRON BEAM WAVE SIGNAL FREQUENCY CONVERTERUTILIZING BEAM DEFLECTION AND BEAM DEFOCUSING Robert Adler, Northfield,Ill., assignor to Zenith Radio Corporation, a corporation of IllinoisApplication November 8, 1954, Serial No. 467,621

17 Claims. (Cl. 250-20) This invention is directed to new and improvedelectron-discharge devices and to wave-signal frequency convertersemploying those devices. :More particularly, the invention is concernedwith electron-discharge tubes in which a beam of electrons is subjectedto deflection control and focus control, in that sequence, in accordancewith two different input signals and with frequency converters utilizingtubes of this type to generate signals representative of theintermodulation products of two signals.

There are a relatively large number of known types of electron tubessuitable for use as frequency converters, modulators, and/ordemodulators; generally speaking, these tubes may be grouped into threeclassifications. In the more common type of converter, a stream ofelectrons is intensity-modulated in accordance with two distinct signalsand is intercepted by an anode coupled to a frequency-selective loadcircuit. The load circuit is made responsive to one of theintermodulation products of the two signals and develops a signalrepresentative of that intermodulation product. Converters of this typeare used in almost all commercially available radio and televisionreceivers as well as in many other applications.

A somewhat less familiar type of converter tube combines intensitymodulation with deflection modulation. In devices of this type, a streamof electrons is first modulated in intensity in accordance with onesignal and is subsequently deflection-modulated in accordance with asecond signal. An output'electrode system, which usuallycomprises a pairof anodes disposed on opposite sides of the undeflected beam path, isemployed to generate an output signal representative of a conversionproduct of the two signals. A specific example of this type ofconversion or modulation system is described and claimed in thecopending application of Robert Adler and John L. Rennick, Serial No.355,476, filed May 18, 1953, now abandoned, and assigned to the sameassignee as the present invention. Other lesserlcnown converter devicesemploy two stagesof deflection control and specialized output electrodesystems to provide the desired frequency conversion.

In all of these prior art converter arrangements, one of the principaldifficulties and disadvantages results from the fact that it isvirtually impossible to completely isolate the two signal-inputelectrode systems from each other; in addition, it is extremelydiflicult to prevent one or both. of the input signals from appearing inunconverted form in the output signal. For example, in conventionalmodulators employing only intensity control, some degree of couplingbetween the two input signal circuits is almost inevitable.This.coupling between the two input systems is highly undesirable inmany applications, such as radio and television receivers, since it maycause variations in the local oscillator frequency or may lead toundesired radiation from the receiver antenna at the local oscillatorfrequency. On the other hand, although the presence of one or both iceof the input signals in the output of the converter is not particularlydisadvantageous in ordinary receiver applications, due to the relativelylarge differences in the frequencies of the desired intermodulationcomponent and the two input signals, this effect may become extremelyimportant in certain applications in which the desired output signal isin the same frequency range as one or both of the input signals.

It is a primary object of the invention, therefore, to provide a new andimproved electron-discharge device, suitable for use in a frequencyconverter, which provides complete isolation of the input signals.

It is another principal object of the invention to provide a new andimproved electron-discharge device and converter system whicheffectively avoid translation of the input signals to the outputelectrode system.

- It is another object of the invention to provide a new and improvedelectron-discharge device which, when incorporated in a frequencyconverter, provides a relatively high conversion gain.

It is a further object of the invention to provide a new and improvedelectron-discharge device and frequency converter having a relativelyhigh signal-to-noise ratio.

It is a corollary object of the invention to provide a new and improvedelectron-discharge device which is relatively simple and economical indesign and construction.

An electron-discharge device constructed in accordance with one aspectof the invention comprises an electron gun for projecting a beam ofelectrons along a given reference path and a deflection-control system,responsive to an applied signal, for deflecting that beam transverselyfrom its reference path as the beam passes through a predeterminedcenter of deflection. The tube further comprises means including anelectron lens for normally focusing the beam to form an image of thecenter of deflection at a preselected subsequent location on thereference path and for varying the location of that image along the pathin response to a second signal. An output electrode system is coupled tothe electron beam and is utilized to derive an output signalrepresentative of transverse excursions of the electron beam from theaforementioned preselected image location.

The electron-discharge device of the invention may also be utilized in adual-conversion system. In some applications, it is desirable to employa signal oscillator for the conversion of a relatively wide range ofreceived signal frequencies; thus, in the television field, it isdesirable to employ a single oscillator for the conversion of receivedsignals ranging in frequency from 54 to 890 megacycles. However, it isextremely difficult to obtain the requisite repeatability in anoscillator operating over such a wide range (approximately to 930megacycles for the usual intermediate-frequency); that is, it isextremely diflicult to tune an oscillator consistently over such a broadband. Accordingly, a single electrondischarge tube adapted to operate aseither a singleconversion or a dual-conversion device may be highlyadvantageous.

It is a further object of the invention, therefore, to provide a new andimproved electron-discharge device and converter in which a singleelectron stream is modulated by three input signals and utilized todevelop an output signal representative of an intermodulation product ofall three of the signals.

It is a corollary object of the invention to provide a new and improvedelectron-discharge tube adapted to operate as either a single-conversionor dual-conversion device.

A dual-conversion electron-discharge device constructed in accordancewith another aspect of the invention cornprises means for projecting abeam of electrons along a given reference path and means for subjectingthat beam to intensity modulation, deflection modulation, and focusmodulation, in the named sequence, in response to three individuallyapplied signals. An output electrode system is included in the device toutilize the thrice-modulation electron beam to derive an output signalrepresentative of an intermodulation product of all three signals. Thethree signals need not all be specifically different from each other;for example, the same signal may be employed for both intensity andfocus modulation.

The features of the invention which are believed to be novel are setforth with particularity in the appended claims. The organization andmanner of operation of the invention, together with further objects andadvantages thereof, may best be understood by reference to the followingdescription taken in conjunction with the accentpanying drawings, inwhich like reference numerals refer to like elements in the severalfigures, and in which:

Figure 1 is a cross-sectional View of an. electron-discharge deviceconstructed in accordance with one embodiment of the invention; thefigure also includes aschematic diagram of a simplified convertercircuit for the tube;

Figure 2 is a perspective view of the electrode structure of the tubeshown in Figure 1;

Figure 3 is an explanatory diagram employed to explain the operation ofthe tube of Figure 1; v

Figures 4 and 5 are graphs illustrating certain operatingcharacteristics of the tube of Figure 1;

Figure 6 illustrates, in cross section, an electron-discharge deviceconstructed in accordance with another embodiment of the invention alongwith asimplified schematic diagram of the associated circuitry in atypical application;

Figures 7A and 7B are graphs which illustrate certain operatingcharacteristics of the lens systems incorporated in the tubes of Figures1 and 6 respectively;

Figure 8 is a schematic diagram of another embodiment of the invention;and

Figure 9 is a schematic diagram of' a dual-conversion embodiment of theinvention.

The wave-signal frequency converter illustrated in Figure 1 comprises anelectron-discharge device 10 including an electron gun 11, adeflection-control system 12, an electron lens sysem 13 and an outputelectrode system 14 all mounted within the usual evacuated envelope 15.Each of the individual electrode systems 11-44 may be entirelyconventional in form; it is the particular combination of these systemswhich forms the basis for the inventive concept. I

Electron gun 11, for example, may include an indirectly-heated cathode16 having an eleotron emissive sun face 17. Gun 11 further includesafocusing. or control electrode 18, including an aperture 19 locatedopposite emissive surface 17, and an accelerator 20 having an aperture2i aligned with aperture 19. Deflection-control systern 12 includes apair of conventional deflector electrodes 22 and 23 suitably disposed onopposite sides of the center plane A of the tube; it will be noted thatall of the electrode sysems in this particular embodiment of the invention are symmetrically arranged with respect to center plane A.

Electron lens system 13 includes three lens electrodes 24, 26 and 28having individual apertures 25, 27 and 29 respectively, the apertures ofthese electrodes being substantially symmetrical with respect to centerplane A. Electrodes 24 and 28 may be formed from sheet metal and areelectrically connected to each. other as by a lead 30. Electrode 26 mayalso be formed from sheet metal; in the illustrated embodiment, however,a simple U-shaped wire is used for this electrode. Output electrodesystem lid comprises a pair of anodes 31 and 32 disposed on oppositesides of the center plane in symmetrical relationship thereto;preferably, a suppressor electrode33 is positioned between the twooutput anodes. v

Preferably, tube 10 employs a sheet-like beam of electrons; that is, theelectron beam viewed in cross section, should have one dimension verymuch larger than the other cross-sectional dimension. As illustrated inFigure 2, the widths of the individual electrode apertures in tube 10are very much smaller than the heights of those apertures, thusproviding an electron beam having a Width which is extremely small ascompared to its height. A sheet beam of this type is preferred becauseit makes possible the control of large beam currents without requiringexcessive control potentials or input signal levels. Figure 2 also givesa more complete pictureof the general configuration and construction ofthe electrodes of tube 10; as indicated in Figure 2., virtuallyall ofthe electrodes for the tube may be formed from sheet metal or wire bysimple stamping or bending techniques.

As shown in Figure 1, cathode 16 of electron gun 11 is connected to aplane of reference potential, here indicated as ground; in thisembodiment of the device, focus electrode 18 is connected to the cathodewithin the tube envelope. Accelerator 20 is connected to a first sourceof positive unidirectional operating potential 8 Dedoctors 22 and 23 arecoupled to a first input or deflection signal source 34 in push-pullmanner and are also connected to a: second source of positive operatingpotential 13 Lens electrodes 24 and 28 are connected to an operatingpotential source B whereas lens electrode 26 is connected to a secondinput or focusing signal source 35 and to an operating potential sourceB Suppressor electrode 33 may be connected to ground, and output anodes31 and 32 are connected to a utilization means comprising a load circuit36. Load circuit 36 may, for example, constitute an output transformerincluding a primary winding 37 connected across the two anodes and asecondary winding 38 having output terminals 39. A tuning capacitor 40may be connected across secondary winding 38. The electrical center of.winding 37 is connected to a source of positive operating potential B toprovide a suitable operating voltage for anodes 31 and 32.

In a typical application, deflection signal source 34 may constitute asource of a modulated carrier wave such as a radio or televisiontransmission signal; thus, source 34 may constitute the antenna andassociated input circuit, including the radio-frequency amplifier ifany, of a television receiver. Focusing signal source 35 may comprisethe local oscillator of such a receiver, and load circuit 36 mayconstitute a part of the input circuit of the firstintermediate-frequency amplifier of that receiver. Operating potentialsources B to B may comprise individual batteries or rectifiers;ordinarily, however, the individual operating potentials are provided byspaced taps on a voltage divider fed by a single source of positiveoperating potential.

When the wave-signal frequency converter illustrated in Figure l isplaced in operation, a stream of electrons is emitted from cathodesurface 17 and is focused into a beam as it passes through aperture 19of electrode 18. The beam is accelerated and projected along a referencepath centered about center plane A as it passes through aperture 21;disregardin any effect of applied signals, the beam continues along thereference path defined by plane A and thus passes between deflectors 22and 23, through lens apertures 25, 27 and 29, and on toward suppressor33. Because/the suppressor electrode is held at cathode potential, thebeam divides as it nears the suppressor and impinges equally upon outputanodes 31 and 32.

The normal operating potentials on deflectors 22 and 23 are equalized sothat, with zero signal from source 34, the clectron bearn is notdeflected from path A. The operating potentials for lens electrodes 24,26 and 28, on the other hand, are adjusted so that in the absence of asignal from source 35 the electron lens formed by these electrodesnormally focuses the electron beam to form an image of P 6 Center ordeflection of system 12 at a preselected subsequent location onreference path A; for the illustrated embodiment, this image locationshouldcoin cide with the plane of output anodes 31 and 32. Ideally, withno signal applied from sources 34 and 35, the electron beam dividesequally between the two anodes; however, this ideal condition is by nomeans essential so long as each anode collects an appreciable portion ofthe beam current. Deflection modulation of the electron beam is effectedby the signal applied to deflectors 22 and 23 from source 34. The focallength of the electron lens formed by system 13, on the other hand,varies in accordance with the signal from source 35.

Operation of the tube as a converter may be more fully understood byreference to Figure 3, in which the various electrode systems of thetube are shown in schematic form. With no signal applied to eitherdeflection system 12 or lens system 13, the electron beam from gun 11 isnot diverted from reference path A and therefore cannot establish apotential difference between anodes 31 and 32. If the signal from source34 instantaneously drives deflector 22 positive with respect todeflector 23, the electron beam is deflected transversely from referencepath A as it traverses the center of deflection 41 of system 12; underthese conditions, the beam follows a deflected path indicated by dashline 42. With lens system 13 adjusted to focus an image of deflectioncenter 41 at a subsequent location on path A approximately in the planeof anodes 31 and 32, as indicated by point 43, the beam continuesthrough the lens and follows the path indicated by dash line 44, passingthrough image location 43. The beam is still centered on the outputanode system so that it develops no potential difference between the twoanodes; thus, no output signal is generated. Similarly, if deflector 23is instantaneously driven positive with respect to deflector 22, thebeam traverses a path gention of a focusing signal from source 35 tolens electrode 26 cannot change the potential difference or currentdistribution between the output anodes, provided the beam is properlycentered to begin with. The only effect that this focusing signal canhave, in the absence of any deflection signal, is to diverge or convergethe beam; the focusing system cannot by itself change the direction ofthe beam and therefore cannot independently cause a signal to begenerated in the output electrode system.

Simultaneous application of input signals to the deflection-control andelectron lens systems, however, gives rise to the desiredfrequency-conversion action. If the beam is deflected from center 41 tofollow path 42, and the focal length of the electron lens is changedsubstantially by varying the potential on lens electrode 26, the beammay be deflected over a range of different paths indicated by dash-dotline 47, line 44, and dash line 48. Similarly, if the beam is deflectedto follow path 45, the resultant path as the beam emerges from theelectron lens may be indicated by lines 49, 46 and 50, depending uponthe focal length of the electron lens as determined by the signalapplied from source 35 to electrode 26 (Figure 1). Looking at thecombined effects of the two control systems from a different standpoint,the voltage on lens electrode 26 may be instantaneously varied from thenormal operating potential supplied by source B so that the focus of theelectron lens coincides with point 51 on reference path A; if the beamis then deflected between paths 42 and 45, the lens reverses the senseof the deflection in the plane of anodes 31, 32. On the other hand, withthe lens adjusted to focus on point 52, the original sense of deflectionispreserved as the beam passes through thelens and continues on to theoutput electrodes.

Thus, the distribution of the beam in the plane of anodes 31 and 32 is afunction of both the input signal applied to deflection system 12 fromsource 34 and the second input signal applied to lens electrode 26 fromsource 35. Two different intermodulation product signals are generatedin the output electrode system; one of these signals has a frequencyequal to the sum of the two input signal frequencies and the other has afrequency equal to the difference between the input signal frequencies.In most applications, however, only the lower of the two beat-frequencysignals is utilized; accordingly, load circuit 36 may be tuned to thisparticular signal frequency so that the higher frequency intermodulationproduct is not translated to succeeding stages in the receiver or otherdevice in which the converter is employed.

Certain of the operating characteristics of tube 10 are illustrated inFigures 4 and 5; in Figure 4, the transconductance of deflection system12 with respect to the output electrodes 31, 32 is plotted as a functionof the instantaneous voltage e on lens control electrode 26. As would beeiipected, the transconductance with respect to both anodes is zero whene is equal to the normal operating voltage applied to electrode 26 fromsource B since this represents an operating condition in which no signalis applied to the lens electrode and the beam is focused to image thecenter of deflection at a point midway between anodes 31 and 32. As thevoltage e is increased or decreased with respect to this normaloperating potential, however, the focal length of the electron lensincreases or decreases so that deflection of the beam gives rise tocorresponding changes in the current distribution between the twoanodes. Of course, any variation in focal length of the electron lenswhich causes the deflected beam to be diverted toward one of the anodesincreases the current drawn by that anode and at the same time decreasesthe current to the other anode, so that the instantaneoustransconductance of the deflection system with respect to one anode isopposite in polarity to the transconductance to the other anode. Thetransconductance g of deflection system 22, 23 with respect to anode 31may be defined as The transconductance characteristic for anode 31 isillustrated by solid line g andthe transconductance characteristic foranode 32 is shown by dash line g32 in Figure 4; as indicated by thesetwo curves, at any given instant the transconductances to the two anodesare equal in magnitude but of opposite polarity.

Figure 5 illustrates the changes in current distribution between the twoanodes in response to changes in deflection voltage e -e for given fixedvalues of e the voltage on lens control electrode 26. With e equal tothe normal operating potential from source 13 of course, the currentdistribution between the two anodes is approximately equal no matterwhat the voltage distribution between deflectors 22 and 23, as indicatedby solid line 54. With the lens control electrode at a higher potentialthan the normal operating voltage, the variations in current to anode 31caused by changes in the deflection voltage is indicated by solid line56. Under the same conditions, the current to anode 32 varies withchanges in deflector voltage as indicated by dash line 55. When thesignal applied to the lens control electrode decreases the potential eon that electrode below the normal operating potential supplied fromsource B the operating characteristics of the two anodes are reversed sothat curve 56 now represents the variations in current to anode 32caused by changes in. the deflector voltages whereas line 55 shows thecurrent drawn by anode 31 with corresponding changes in the potentialson: the'defl ectors.v

The converter system of Figure 1 effectively isolates the two inputsignals from sources 34 and 35 from each other and at the same timeprevents translation of either of the input signals to output electrodesystem 14. Deflectors 22 and 23 are shielded from the lens controlelectrode 26 by lens electrode 24, which is maintained at a constantpotential, so that there can. be no direct electrostatic couplingbetween the deflection-control and focus-control systems. Virtually noneof the electrons of the beam are reflected from lens system 13 backtoward deflection system 12, so that there can be no coupling byreflection; furthermore, there can be no space-charge coupling betweenlens control electrode 26' and deflection system 12. As indicated in theforegoing explanation of Figure 3, neither of the two input signals cangenerate any output signal in system 14 in the absence of the other, sothat neither input signal can be translated inunmodulated form to anodes31, 32. The converter utilizes both half cycles of the input signals, sothat it is easily possible to obtain a relatively high conversion.transconduct'ance.v

Figure 6 illustrates another embodiment of the electrondischarge deviceof the invention incorporated in a color converter or demodulator for a.color television receiver. The color demodulator comprises anvelectron-discharge device 60 including an electron gun 11, adeflection-control system 12, an electron lens system 63 and an outputelectrode system 64 all mounted within the usual evacuated envelope 15.Gun 11 and deflection control system 12 may be essentially identical inconstruction with the similarly-numbered systems in tube accordingly, adetailed description of these portions of tube 60 need not be repeated.

Electron lens system 63 comprises a lens control electrode 66 which maybe essentially similar in construction to lens electrode 26' of tube 10and includes an. aperture 67 aligned with the center plane A of tube 60.The lens electrode system further includes a helical grid 65 mounted ona pair of support rods 68 and encompassing lens control electrode 66. Ineffect then, the two sides 69 and 75 of grid 65 constitute two lenselectrodes or lens grids disposed on the opposite sides of lens controlelectrode 66.

Output electrode system 64 of tube 60 comprises a pair of anodes 71 and72. disposed on opposite sides of center plane A. Anode 72 is mounted sothat one edge 73 coincides with the center plane; the other anode 71includes a projection 74 which extends behind anode 72 across centerplane A.

The cathode 16 of tube 60 is connected to ground and focus electrode 18is maintained at a potential slightly negative with respect to thecathode by means of. a battery or other source of unidirectionalpotential 75. As in the previous embodiment, accelerator is connected toa first source of positive unidirectional, operating. potential 13Deflectors 22 and 23 are coupled in push-pull relationship to the colorvideo signal circuits 76 of a color television receiver and toa secondsource of. positive operating potential 13 Circuit 76 may include anygroup of conventional devices. for intercepting and detecting a colortelevision broadcast to generate a composite color signal including theusual color synchronizing components and a carrier color signal. Lenscontrol electrode 66 is coupled to the usual color referenceoscillator77 and to a suitable source of positive operating potential Breferenceoscillator 77 is also coupled: to color video signal circuits76. Lens grids69 and 70 are connected to a source of positive DCpotential B Anode. 71 is con.- nected to a first load circuit 78; loadcircuit 78 may include a load. resistor 79 interconnecting anode 71. anda source of positiveoperating potential 3 the output from theloadcircuit being obtained from. an. output termir nalldfl. Anode'72.is..connected. to a. second load circuit81' comprising an outputterminal 83 and a load resistor 82 interconnecting; the anode 72 and anoperating potential source 3 The operational characteristics of theconverter of Figure 6, including. tube 60, are essentially similar tothose of the apparatus of Figure 1. As in the previously describedembodiment, electron gun 11 generates and projects a focused" stream of.electrons along a center plane A between deflect'ors 22 and 23, throughgrid 69', aperture 67, and grid 70, to impinge upon the two outputelectrodes. For normal operation, the operating potentials on thevarious electrodes are adjusted so that the beam is divided equallybetween anodes 71 and 72 and the electron lens formed by system 63focuses the beam to form an image of the. center of. deflection ofsystem 12 at edge 73 of anode 72.

Application of a deflection signal to system. 12 cannot by itselfproduce any outputsignal in the utilization means comprising load.circuits 78 and 81, since electron lens system. 63 effectivelyobliterates the deflection-modulation applied to the beam in system 12by redirecting the beam so that it isdivided between anodes 71 and 72 inthe same ratio as when. no deflection signal is present. On the otherhand, variations in. the focal length of the electron lens do not giverise to any output signal in the absence of a deflection signal, sincethe beam continues to be centered about path- A. and impinges upon thetwo anodes in the sameratio as if the lens remained unchanged. Thus, thedemodulator illustrated in Figure 6 effectively precludes translation ofeither of the input signals from circuits 76 and 77 to load circuits 78and 81 and effectively limits the output signal to the intermodulationproducts of the twoinput signals. In the illustrated embodiment,deflection-control system' 12' is made responsive to the carrier colorsignal component of the received color telecast whereas. the focallength of the electron lens formed by system 63- is varied in accordancewith the usual color reference signal generatedby oscillator 77 andcontrolled in phase and frequency by the color synchronizing signalsincluded in the received composite color signal. The complete isolationof the output electrode system from both theinput signals isparticularly valuable in this application, since the input signals arenot widely separated in frequency fromthe desired color-differenceoutput signals. In addition; as in the apparatus of Figure I, the twoinput signals are: completely isolated from each other so that the colonreference signal cannot be reflected back into video circuits176 and thecarrier color signal is not applied to: oscillator 77.

There are, however, some differences between tube 10 of: Figure l andtube 60. of Figure 6. The principal difference between these two devicesresults from the different types of electrodes employed in lens systems13 and 6-3. Each of these structures, it. is true, comprises what iscommonly called a unipotential lens system; that is, the lens systemincludes two electrodes maintained at acommonpotential and located onopposite sides of a third lens electrode which is maintained at adifferent potential; The electron lens formed by system 13 is always aconvergent lens, however, whereas lens electrode system 63' may formeither a convergent or a divergent electron lens.

In. Figure 7A, the refractive power of the electron lens formed by lenssystem 13 is plotted as a function of the voltage 2 on electrode. 26. Aswould be expected, the refractive power of the lens is.zero when e isequal to the voltage applied to electrodes 24 and 28from source B sinceunder those conditions no effective electron lens isformed. As 0 isincreased or decreased from that particular value, an electron lens ofincreasing refractive power is developed; the resulting curve 89 showingrefracti'vepower ofthe' lens. versus voltage e is similar inconfiguration to a. parabola. In order to provide a useful operatingrange for the lens, the normal potential on electrode" 26 supplied fromsource B3+ is established either substantially lower than the potentialfrom source 3 as indicated by line 90, or is made considerably higherthan the potential of source B.,-}-, as indicated by line 91. If thenormal operating potential of the lens control electrode is establishedat the value indicated by line 90, any increase in e 5 caused by thesignal from source 35 reduces the refractive power of the lens andincreases its focal length, whereas decreasing voltage e shortens thefocal length of the lens. With a higher value for 13 as indicated byline 91, increases in lens control voltage a increase the refractivepower of the lens and shorten the focal length of the lens, whereas anydecrease in the control voltage increases the focal length of the ens.

- Figure 7B provides a graph of the refractive power of the lens formedby system 63 of tube 60 plotted as a func tion of the voltage e on lenscontrol electrode 66. As in the case of lens system 13, of course, therefractive power of the lens is zero whenever voltage 0 is equal to thevoltage applied to grids 69 and 70 from source 13 since when there is nopotential difference between these elements no lens is formed. Asindicated by line 93, the refractive power of the lens formed by system63 may be either positive or negative and is an essentially linearfunction of lens control voltage 2 in other words, the electron lensformed by system 63 may be either a convergent or divergent lensdepending upon the potential of electrode 66 as compared to the voltageon grids 69 and 70. Usually, it is preferable to adjust the voltage fromsource B to some value lower than that from source 13 so that the normaloperating condition for the lens is indicated by line 94, thus forming anormally convergent lens. The signal voltage applied to electrode 66from oscillator 77 may then be utilized to shorten the focal length ofthe lens by reducing the total lens electrode potential e or to increasethe focal length of the lens by increasing voltage e For someapplications, lens electrode system 63 is somewhat more advantageousthan lens system 13 since changes in the focal length of the lens are alinear rather than a parabolic function of the applied control voltageand the lens is somewhat more sensitive to voltage changes, which maypermit the use of a focusing signal source having a lower outputamplitude. On the other hand, in other applications, lens system 13 maybe preferable since it introduces less partition noise in the outputsignal and slightly less loss of gain due to current drawn by the lenselectrodes. Both lens electrode systems, however, are quite satisfactoryfor most applications.

Figure 8 illustrates a further embodiment of the invention in whichdeflection control is obtained by use of a transverse-modetraveling-wave structure. The frequency converter tube 100 comprises anelectron gun 101, a traveling-wave deflection-control system 102, a lenselectrdde system 103, and an output electrode system 104 positioned inthat order within a conventional evacuated envelope 15. Gun 101 mayinclude a cathode 106, a focusing electrode 107, an accelerator 108 anda beamlimiting electrode 109; electrodes 1117-409 each include anaperture symmetrically encompassing the center plane or beam referencepath A of the tube. Deflection-control system 102 comprises a pair oflow-velocity wave-transmission lines 112 and 113 arranged on oppositesides of center plane A. Transmission line 112 may include a helicalconductive winding 114 and a plurality of guiding field electrodes 115interposed between winding 114 and reference path A. A terminatingresistance element 116 may be disposed closely adjacent the end ofwinding 114 opposite electron gun 101. Wave-transmission line 113 is ofsimilar construction and includes a helical conductive winding 117, aplurality of guiding field electrodes 118, and a resistance load element119 corresponding to components 114, 115 and 116 of line 112respectively.

system 13 of tube 10 (Figure 1) and includes a pair of apertured lenselectrodes 124 and 128 disposed on opposite sides of lens controlelectrode 126. In this particular embodiment, lens electrodes 124 and128 comprise opposite sides of a conductive boX surrounding lenselectrode 26. Output electrode system 104 includes a pair of receptorelectrodes 131 and 132 disposed on opposite sides of reference path Aclosely adjacent to the reference path. The output electrode systemfurther includes a collector electrode 133.

Cathode 106 of gun 101 is connected to ground, as is focus electrode107; in any given tube design, it may be desirable to operate the focuselectrode slightly above or slightly below the potential of the cathodein which case the focus electrode should be provided with a separateexternal lead. Accelerator 108 is connected to a first source ofpositive unidirectional operating potential 13 and beam-definingelectrode 109 is connected to a second source of D. C. potentialB-,,-{-. The ends of conductive windings 114 and 117 adjacent gun 101are connected in push-pull to a deflection signal source 134; the twotransmission-line windings are also connected to a source of positiveoperating potential 3 Guiding field electrodes and 118 are all connectedto each other and to a source of positive operating voltage 8 Theconnections for lens system 103 are essentially similar to those for thepreviously described lens system 13; lens control electrode 126 isconnected to a focus signal source and to an operating potential sourceB whereas lens electrodes 124 and 123 are connected to a source ofpositive operating potential 13 In output electrode system 104,collector 133 is connected to a source of D. C. potential 13 The tworeceptor electrodes 131 and 132 are coupled to the opposite ends of aprimary winding 137 of an output transformer included in a load circuit136. Load circuit 136 further includes a secondary winding 138 which maybe tuned by means of a capacitor 140; the terminals 130 of winding 138comprise the output terminals for load circuit 136. The electricalcenter of primary winding 137 is connected to a D. C. operatingpotential source 13 to provide suitable unidirectional operatingpotentials on receptors 131 and 132.

In many respects, the converter illustrated in Figure 8 operates in thesame manner as the apparatus of Figures 1 and 6. In electron gun 101, astream of electrons emitted from cathode 106 is focused, accelerated,and limited in width to form a beam of electrons projected alongreference path A. As the beam enters the portion of the reference pathbounded by transmission lines 112 and 113, it is subjected to atransverse field controlled by a signal applied to windings 114 and 117from source 134. As the beam passes the first part of thewave-transmission lines, it absorbs signal energy from the lines and isdeflected transversely from path A in response to that signal energy.The transverse excursions of the beam in turn induce a signal back inthe wave-transmission lines as the beam continues along its path; mutualinteraction between the beam and the signal Wave on the lines substantially amplifies the input signal. The electron beam is confined betweenthe transmission lines by a periodic electrostatic lens fieldestablished by maintaining electrodes 115 and 118 at a substantiallydifferent operating potential from the operating potential applied tothe conductive windings. Thus, the deflection system 102 functions as atransverse-mode traveling-Wave device of the type described and claimedin the copending applications of Robert Adler, Serial Nos. 394,797 and394,798, both filed November 27, 1953, and assigned to the same assigneeas the present invention. The operation of a traveling-wave system ofthis type is explained in detail in those two applications and need notbe examined at great length here. For the purposes of this application,it is sufficient Lens electrode system 103 is essentially similar tolens 75 to indicate that the overall effect of deflection system 102 1 1upon the beam is to deflect it transversely from path A in response tothe signal from source 134; the eflective center of deflection of thesystem is very close to the ends of transmission line 112 and 113adjacent lens system 1133. The deflection system may be constructed toprovide very favorable noise properties, as compared to conventionaldeflectors, and is therefore highly advantageous in a converter utilizedas a first detector in a television receiver or similar apparatus. Theresistive elements 116 and 119 are employed only to load the linessufficiently to prevent reflections of signal energy back along thewave-transmission lines; no signal output is taken from the conductivewindings.

Lens system 103 operates in exactly the same manner as system 13; itfocuses the electron beam to form an image of the center of deflectionof system 1912 approximately at the center of output electrode system104. As in the previously described embodiments, the focal length of theelectron lens formed by system 1113 is varied in accordance with aninput signal from source 135 so that the position of the beam as ittraverses the space between receptors 131 and 132 is a function of aninterrnodulation product of the two input signals from sources 134 and135. The output electrode system in turn generates a signalrepresentative of transverse excursions of the beam from the imagelocation on path A and supplies that signal to the utilization meanscomprising load circuit 136. Receptors 13.1 and 132 are inductivelycoupled to the beam; the collector 133 is employed as the "terminalelectrode of the system. While anodes such as electrodes 31 and 32(Figure 1) might be employed in place of receptors 131 and 132, it hasbeen found that the receptors provide somewhat less noise in the outputsignal when employed in combination with a properly constructedtraveling-wave tube deflection system such as system M2 or with acomposite electrostatic deflection system of the type described andclaimed in the copending application Robert Adler, Serial No. 452,620,filed August 27, 1954, and assigned to the same assignee as the presentinvention.

The embodiment of Figure 8 retains all of the advantages of theconverters described in connection with Figures l and 6 and may alsoprovide an improved signal-tonoise ratio in the output signal ascompared to conventional intensity-control converters and devicesutilizing ordinary deflectors. Because amplification of the signal wavetraveling down the transmission lines does not contribute directly tothe output signal, the transmission lines may be made substantiallyshorter than in traveling-wave tubes in which the output signal isderived from the conductive windings; it is only the transverseexcursions of the beam which have any effect upon the ultimate outputsignal. Although tube 1% is somewhat more complicated in constructionthan the previously described embodiments of the invention, it maynevertheless be economically advantageous for particular applicationswhere noise problems and low input signal levels are important factors.

Figure 9 illustrates another embodiment of the invention comprising atwo-stage or dual-frequency converter. This dual-conversion systemincludes an electron-discharge device It? which may be essentiallyidentical in construction with the tube illustrated in Figure 1 and maycomprise an electron gun 11, a deflection-control system 12, a lenselectrode system 13, and an output electrode system 14 all mountedwithin evacuated envelope 15. As before, gun 11 includes a cathode 16, acontrol electrode 18, and an accelerator 21?. Deflection system 12includes a. pair of deflectors 22 and 23 disposed on opposite sides ofthe reference path A of the tube and lens system 13 comprises a lenscontrol electrode 26 positioned between a pair of lens electrodes 24 and28. As before, the output electrode system includes a pair of anodes 31and 32 disposed on opposite sides of reference path A; preferably,

a suppressor electrode 33 is positioned between the two The circuitconnections for tube 10 are also quite similar to those of Figure 1;cathode 10 is grounded, accelerator 11 is connected to D. C. source Band deflectors 22 and 23 are coupled to a deflection signal source 34and to a second source of positive operating potential B3+. Lenselectrodes 24 and 28 are connected to each other and to an operatingvoltage source 13 whereas lens electrode 26 is coupled to focusingsignal source 35 and to D. C. source B As before, suppressor 33 isgrounded and anodes 31 and 32 are connected to load circuit 36 and tooperating potential source 13 The principal difference between theembodiment of Figure 9 and that of Figure 1 results from the fact that alead for control electrode 18 is brought out separately from the lead oncathode 16 and the control electrode is coupled to focusing signalsource 35 through a coupling capacitor 150. A switch 151 is interposedin the circuit interconnecting source 35 and control electrode 18, and asource of bias potential, indicated by battery 152 and choke coil 153,is utilized to return the control electrode to cathode 16. In a typicalapplication, deflection signal source 34 may comprise the antenna andinput circuits, with or without a radio-frequency amplifier, of atelevision receiver and focusing signal source 35 may constitute thelocal oscillator for the receiver, tube 10 being employed as theconverter or first detector of the receiver.

With switch 151 open, the converter of Figure 9 operates in exactly thesame manner as the apparatus 'illus trated in Figures 1 and 6. Gun 11generates and projects a beam of electrons along path A; the beam isdeflected transversely from the reference path, as it traverses thecenter of deflection of system 12, in response to the signal applied todeflectors 22 and 23 from source 34. The operating potentials on theelectrodes of lens system 13 are adjusted to establish an electron lenswhich focuses the beam to form an image of the center of deflection at asubsequent location on path A approximately in the plane of anodes 31and 32 so that the beam normally divides equally between the two anodes.The signal applied to lens electrode 26 from source 35 varies the focallength of the electron lens, and output electrode system 14 utilizes thedeflection-modulated and focus-modulated beam to generate an outputsignal comprising the intermodulation products of the signals fromsources 34 and 35. This output signal appears in load circuit 36 and, ina typical receiver application, is supplied to the subsequentintermediate-frequency stages of the receiver.

In a television receiver adapted for operation in both the V. H. F.(54-216 megacycle) and U. H. F. (470-890 megacycle) bands, the converterof Figure 9 may be operated as a single-conversion device in the V. H.F. range. However, ifit is desired to use a single local oscillator asfocusing signal source 35, it becomes highly desirable to reduce thefrequency range required for the oscillator. For operation in the U. H.F. band, therefore, switch 151 is closed to complete the circuitcoupling focusing signal source 35 to control electrode 18. Under theseconditions, the electron beam is first intensity-modulated by the localoscillator signal from source 35, then deflectionmodulated by thereceived television signal from source 34, and subsequentlyfocus-modulated by the local oscillator signal from source 35. Thethrice-modulated electron beam is intercepted by anode system 14 whichdevelops an output signal representative of the intermodu' lationcomponents of the three signals. A

The dual-conversion action of the converter of Figure 9 with switch 151closed may be shown by considering the effect of the individual signals.In the absence of any signal on deflection system 12 and lens system 13,in tensity-modulation of the beam by the signal applied to controlelectrode 18 from source 35 cannot produce any output signal inelectrode system 14, since, anodes 31 and 32 still intercept the samerelative proportions of the electron beam, and no change in currentdistribution or potential diiference between the two anodes isestablished.

As indicated by the foregoing description of operation of thedeflection-control'and electron lens systems, the signals applied tothose systems cannot independently develop an output signal in system14. With all three signals supplied to tube 10, however, the beamapproaches anodes 31 and 32 from a direction determined by the conjointefiect of the deflection signal applied to electrodes 21 and 22 and thefocusing signal applied to lens control electrode 26; at the same time,the beam is modulated in intensity by the signal applied to controlelectrode 18. Thus, the output signal developed by system 14 is a product of all three of the input signals.

In order to indicate more explicitly the advantages of thedual-conversion arrangement shown in Figure 9 with regard to thefrequency range required for signal source 35, U. H. F. channel 69,havinga carrier frequency of 801.25 megacycles,-will be considered asaspecificexample. If the usual intermediate-frequency of 41.25 megacyclesis to be employed, the oscillator frequency utilized in conventionalsignal conversion systems is 842.50 megacycles. For the dual-conversionsystem shown in Figure 5, however, a local oscillator frequency of421.25 megacycles may be employed. Using this frequency, the beatbetween the television carrier and the local oscillator signal in theintensity and deflection modulation systems produces an intermodulationcomponent having a frequency of 380 megacycles and the beat frequencybetween this intermodulation component and the local oscillator signalapplied to lens system 13 produces an ultimate intermodulation producthaving a frequency of 41.25 megacycles. Thus, the oscillator frequencyrequired for conversion of the channel 69 signal to the desiredintermediate-frequency signal is effectively cut in half, and anoscillator having an operating range of approximately 100 to 465megacycles may be employed to cover the full V. H. F.-U. H. F.television range instead of one having a range of about 100 to 930megacycles as would be necessary with a single-conversion system. Thedevice retains all of the isolation advantages obtained when used in asingle-conversion system; the possible coupling between lens electrode26 and control electrode 18 is quite harmless since they are connectedto the same signal source.

In order to facilitate a more complete understanding of theelectron-discharge devices of the invention, the dimensions andelectrical parameters for a specific tube corresponding to tube ofFigures 1 and 9 are set forth hereinafter. This data is presented merelyby way of illustration and in no sense as a limitation upon the tubestructure.

Dimensions Inch Height of tube electrodes .563 Width of slot 19 .015Width of slot 21 .015 Spacing between deflectors 22, 23 .024 Width ofslots 25, 29 .025 Width of slot 27 .033 Spacing between anodes 31 and 32.035

Figure 1 is drawn approximately to scale.

Operating voltages Cathode 1 ground Control electrode 18 volts -1Accelerator 20 do 250 Deflectors 22, 23 -1 do 74 Lens electrodes 24, 28do 135 Lens electrode 26 do 51 Anodes 31, 32 do 250 Suppressor 33 groundOperating currents Accelerator 20 milliamperes 0.5 Lens electrodes 24,28 microamperes 160 .Lens electrode 26 do 17 Anodes 31, 32..-milliamperes 1.5

This particular tube has been successfully operatedas a first detectorfor a television receiver.

Electron-discharge devices and converter systems constructed inaccordance with the invention are relatively simple and convenient inconstruction and present marked advantages as compared to moreconventional devices. Complete isolation between the input signals iseasily obtained and, in the single-conversion embodiments, no individualinput signal is separately translated to the output electrode system.Relatively high conversion gains are obtainable in all of theillustrated embodiments of the invention. The devices of Figures 8 and 9present particular advantages with respect to noise reduction andoscillator range respectively.

While particular embodiments of the present invention have been shownand described, it is apparent that changes and modifications may be madeWithout departing from the invention in its broader aspects. The aim ofthe appended claims, therefore, is to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

I claim:

1. A wave-signal frequency converter comprising: means for projecting abeam of electrons along a given reference path; means for subjectingsaid beam of electrons to deflection modulation and to focus modulation,in the named sequence, in response to two individual signals; andanoutput electrode system for utilizing the twice-modulated electron beamto derive an output signal representative of an inter-modulation productof the two input signals.

2. A dual-conversion electron-discharge device comprising: means forprojecting a beam of electrons along a given reference path; means forsubjecting said beam to intensity modulation, deflection modulation, andfocus modulation, in the named sequence, in response to threeindividually applied signals; and an output electrode system forutilizing the thrice-modulated electron beam to derive an output signalrepresentative of an intermodulation product of all three signals.

3. A dual-conversion wave-signal frequency converter comprising: meansfor projecting a beam of electrons along a given reference path; anintensity-control electrode, a deflection-control system, and anelectron lens system disposed in the order named along said referencepath; means for applying a first input signal to said deflection-controlsystem to deflection-modulate said beam; means for applying a secondinput signal to said intensity-control electrode and to said electronlens system to intensity-modulate and focus-modulate said electroubeam;an output electrode system, coupled to said electron beam, for derivingan output signal from said thrice-modulated electron beam; andutilization means, responsive to a dual-intermodulation product of saidfirst and second input signals, coupled to said output electrode system.

4. An electron-discharge device comprising: an elec tron gun forprojecting a beam of electrons along a given reference path; adeflection-control system, responsive to an applied signal, fordeflecting said beam transversely from said reference path as said beampasses through a predetermined center of deflection; an output electrodesystem, coupled to said electron beam, for deriving an output signalrepresentative of transverse excursions of said beam from said path at apreselected image location spaced from said deflection system; and meansfor varying the effective transconductance of said deflection systemwith respect to said output electrode system over a predetermined rangeincluding values of opposite polarity, said means comprising an electronlens system interposed between said deflectioncontrol system and saidoutput electrode system for normally focusing said beam to form an imageof said center of deflection at said preselected image location and forvarying the position of said image along said path in response to asecond signal.

'5. An electron-discharge device Constructed in accordance with. claim 4in which said electron lens system comprises three lens electrodesarranged in sequence along said reference path.

6. An electron-discharge device constructed in accordance with claim 4in which said electron lens system comprises three lens electrodesarranged in sequence along said reference path with the first lenselectrode in said sequence electrically connected to the last lenselectrode in said sequence to establish a unipotential electron lens.

7. An electron-discharge device constructed in accordance with claim 4in which said electron lens system comprises a pair of apertured lenselectrodes each substantially encompassing a predetermined portion ofsaidreference path.

8'. An electron-discharge device constructed in accordance. with claim 4in which said electron lens comprises a first lens grid, an aperturedlens electrode, and'a second lens grid arranged in the order named alongsaid reference path.

9. An electron-discharge device constructed in accordance with claim 4in which said output electrode system comprises a pair ofbeam-intercepting anodes symmetrically arranged on opposite sides ofsaid reference path ad'- jacent said preselected imagelocation.

10. An electron-discharge device constructed in accordance with claim 4in which said output electrode system comprises a pair of receptorelectrodes symmetrically arranged on opposite sides of said referencepath adjacent said preselected image location in inductive couplingrelationship to said beam.

11. An electron-discharge device constructed in acc'ordance with claim 4in which said electron gun comprises a control electrode for varying theintensity of said beam in response to an applied signal.

12. An electron-discharge device constructed in accordance with claim 4in which said deflection-control system comprises a pair of low-velocitywave-transmission lines disposed on opposite sides of said referencepath.

13. A wave-signal frequency converter comprising: an electron gun forprojecting a beam of electrons along. a given reference path; adeflection-control system, responsive to an applied signal, fordeflecting said beam transversely from said reference path as said beampasses through a predetermined center of deflection; an output electrodesystem, coupled to said electron beam, for deriving an output signalrepresentative of transverse excursions of said beam from a preselectedimage location on said reference path spaced from saiddeflection-control system; means for varying the effectivetranscondu'ctance of said deflection-control system with respect to saidout- 16 a put electrode system over a predetermined range includingvalues of opposit'epolarity', said means comprising an electron lenssystem interposed between said defiectioncontrol system and said outputelectrode system for normally focusing said beam to form an image ofsaid center of deflection at said preselected image location and forvarying the position of said image along said path in response to asecond signal; means for applying a first input signal to saiddeflection-control system; means for applying a. second input signal tosaid electron lens system; and utilization means, responsive to anintermodulation product of said input signals, coupled to said outputelectrode system.

14. A wave-signal frequency converter constructed in accordance withclaim 13, in which said output electrode system comprises a pair ofoutput electrodes coupled to said electron beam and in which saidutilization means comprises a resonant load circuit, tuned to thefrequency of said intermodulation product, interconnecting said pair ofoutput electrodes.

15. A wave-signal frequency converter constructed in accordance withclaim 13, in which said output electrode system comprises a pair ofbeam-intercepting anodes and in which said utilization means comprises apair of load circuits individually interconnected to said anodes.

16. A wave-signal frequency converter constructed in accordance withclaim 13, in which said electron gun ineludes a control electrode forcontrolling the intensity of said electron beam, said converter furtherincluding means for applying a third input signal to said controlelectrode, and said utilization means being responsive to anintermodulation product of said three input signals.

17. A wave-signal frequency converter constructed in accordance withclaim 13, in which said electron gun includes a control electrode forcontrolling the intensity of said electron beam, said converter furtherincluding means for applying said second input signal to said controlelectrode as well as to said electron lens system, and said utilizationmeans being responsive to a dual-intermodulation product of said inputsignal.

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